Postman API Testing: Writing Test Scripts for REST Endpoints

// Test scripts run after the response is received
// Written in JavaScript using the pm.* API

// 1. Assert status code
pm.test("Status code is 200", function () {
    pm.response.to.have.status(200);
});

// 2. Assert response body has required fields
pm.test("Response has user data", function () {
    const jsonData = pm.response.json();
    pm.expect(jsonData).to.have.property("id");
    pm.expect(jsonData).to.have.property("email");
    pm.expect(jsonData).to.have.property("name");
});

// 3. Assert response time
pm.test("Response time is acceptable", function () {
    pm.expect(pm.response.responseTime).to.be.below(500);
});

// Expected test output:
// ✓ Status code is 200
// ✓ Response has user data
// ✓ Response time is acceptable

// 4. Validate array responses
pm.test("Returns array of users", function () {
    const jsonData = pm.response.json();
    pm.expect(jsonData).to.be.an("array");
    pm.expect(jsonData.length).to.be.at.least(1);

    jsonData.forEach(user => {
        pm.expect(user).to.have.all.keys("id", "email", "name", "created_at");
    });
});

// 5. Assert content type header
pm.test("Content-Type is JSON", function () {
    pm.response.to.have.header("Content-Type", "application/json");
});

// 6. Assert error response structure
pm.test("Error response has correct format", function () {
    const jsonData = pm.response.json();
    pm.expect(pm.response.code).to.equal(400);
    pm.expect(jsonData).to.have.property("error");
    pm.expect(jsonData.error).to.be.a("string");
});

// Expected output:
// ✓ Returns array of users
// ✓ Content-Type is JSON
// (error test only runs on 400 response)

// 7. Validate response against JSON Schema
const userSchema = {
    "type": "object",
    "required": ["id", "email", "name", "created_at"],
    "properties": {
        "id": {"type": "integer"},
        "email": {"type": "string", "pattern": "^[\\w.-]+@[\\w.-]+\\.\\w{2,}$"},
        "name": {"type": "string", "minLength": 1},
        "created_at": {"type": "string", "format": "date-time"}
    }
};

pm.test("Response matches user schema", function () {
    const jsonData = pm.response.json();
    pm.response.to.have.jsonSchema(userSchema);
});

// 8. Test with dynamic data using environment variables
pm.test("Created user has unique ID", function () {
    const jsonData = pm.response.json();
    // Store for later tests
    pm.environment.set("created_user_id", jsonData.id);
    pm.environment.set("created_user_email", jsonData.email);
});

// Expected output:
// ✓ Response matches user schema
// ✓ Created user has unique ID

// Pre-request scripts run BEFORE the request is sent

// 1. Generate dynamic test data
const timestamp = Date.now();
pm.variables.set("unique_email", `test-${timestamp}@example.com`);
pm.variables.set("unique_name", `Test User ${timestamp}`);

// 2. Set authentication token
const token = pm.environment.get("auth_token");
if (token) {
    pm.request.headers.add({
        key: "Authorization",
        value: `Bearer ${token}`
    });
}

// 3. Add random data for idempotency
pm.variables.set("idempotency_key",
    require('uuid').v4 ? require('uuid').v4() : Math.random().toString(36)
);

// The request body will use {{unique_email}} and {{unique_name}}
// which are resolved at runtime

// 9. Test with response headers
pm.test("Rate limit headers present", function () {
    pm.response.to.have.header("X-RateLimit-Limit");
    pm.response.to.have.header("X-RateLimit-Remaining");

    const remaining = parseInt(pm.response.headers.get("X-RateLimit-Remaining"));
    pm.expect(remaining).to.be.at.least(0);
});

// 10. Conditional tests
const statusCode = pm.response.code;
if (statusCode === 200) {
    pm.test("Successful response data", function () {
        const jsonData = pm.response.json();
        pm.expect(jsonData.data).to.be.an("array");
    });
} else if (statusCode === 404) {
    pm.test("Not found message", function () {
        pm.expect(pm.response.json().error).to.include("not found");
    });
}

// 11. Logging for debugging
console.log("Response time:", pm.response.responseTime + "ms");
console.log("Response body preview:", JSON.stringify(pm.response.json()).slice(0, 200));